Excellent work indeed. My max render size is 1600 px. Quite a while ago I rendered the same image in different sizes and sent them to a photo lab to make A4 (roughly Legal) sized images. I also printed them to this size and found that there is no difference if I increased the size. Only when I do spherical panoramas, I render the 6 cube faces as 2560 px to assemble to a 8192 x 4096 px panorama.